And thus, Microsoft bites itself in its behind with Metro. As you all surely know by now, the Metro environment in Windows 8, and its accompanying applications, need to follow a relatively strict set of rules and regulations, much like, say, applications on iOS. For one type of application, Metro has already proven to be too restrictive and limited: web browsers. Microsoft has had to define a separate application class [.docx] - aside from Metro and desktop applications - just to make third party web browsers possible for Windows 8.

WinRT is built on top of Win32, so the latter isn't going anywhere. At best, it might become inaccessible to third-party developers at some point.

But this speaks to the issue with third-party browsers, which is that as web clients become increasing rich application platforms with open-standard APIs for accessing native device functionality, it makes more sense for the web client to be tightly integrated with the OS and the underlying device hardware and not open to third-party implementations.

In other words, the IE 10 web client is now effectively a large subset of the native runtime environment on Windows 8, and there are substantial benefits in having one common runtime stack.

Hence Boot2Gecko. If you want a Mozilla stack, use the Mozilla stack. Otherwise choose the Microsoft, Apple, Google (ChromeOS or Android), or Amazon stacks. Or fork one of the open stacks and scratch your itch.